The in-game server browser does that to me too. Even when it does work I only get around 50 servers that show up. Try using a program like "Gamespy" or the "All Seeing Eye." I personally use the "All Seeing Eye" and I get a lot more servers about 450-500 on JK2 and more accurate pings.

This has happened to a few others including myself. There are times when it works fine, other times no list at all. I have tried things without sucess. Disconnecting then reconnecting, Restarting the computer, when I dont get a server, I go back to Wolfenstien without any server list problems.
No Idea.